I had one long ago, I gave it to my older brother to hang on his wall. The previous owner had removed the rear sight, if it ever had one, so the threaded in barrel would be obviously visible.
I never tried putting anything in the chamber, but the magazine would not hold a regular rimless cartridge so I figured it was for a rimmed cartridge or a very fat rimless of some sort.
I've recently read of gallery practice cartridges for some smoothbore training rifles, they used a short case and some used a light bullet with fin stabilization. Power level was about like a .22, maybe less.
Later on I'll have my brother bring the rifle here so I can take some photos, its in pretty good shape other than the missing rear sight.